Chapter 5: Emerging Infectious Diseases

Emergence of Infectious Disease Causes of emerging infectious disease – Pathogens identified in a human population for the first time – Pathogens occurring previously but now increasing in incidence or expanding into other areas Microbes are the major cause of death in developing countries.

Factors Affecting Disease Emergence Bacteria can evolve to decrease their exposure to antibiotic concentrations. – Bacterial biofilms, fimbriae, efflux pumps, chromosomal changes Climate change Overcrowding and urbanization Globalization Zoonotic diseases Immunosuppressive drugs Antigenic drift Antigenic shift Growing number and virulence of vectors

Our Losing War Against Pathogenic Microorganisms Bacteria develop resistance to antibiotics through: – Chromosomal mutation – Inductive expression of latent chromosomal gene – Exchange of genetic material through transformation, transduction, or conjugation Staphylococcus aureus has resisted and evolved to such an extent that is responsible for millions of deaths.

Emerging Food- and Waterborne Pathogens Imported to United States from other countries Cyclospora cayetanensis E. coli O157:H7 Vibrio cholerae Campylobacter jejuni Listeria monocytogenes

Emerging Pathogens in the Immunocompromised Conditions involving compromised immunity enable pathogen survival at higher incidences in a community. Mycobacterium tuberculosis has infected 2 billion people worldwide. Candida albicans, Aspergillus fumigates, and Cryptococcus neoformans are oppportunistic fungal pathogens in HIV patients.

Vector-borne Emerging Infectious Diseases (1 of 2) Increasingly threatening group of diseases WHO has been working toward their elimination. Examples include malaria, Lyme disease, Dengue hemorrhagic fever. Next slide shows life cycle of malaria.

Vector-borne Emerging Infectious Diseases (2 of 2) Figure 5-7 The life cycle of malaria. Source: Picture courtesy of the Centers for Disease Control and Prevention. Retrieved March 21, 2010, from

Parasites That Survive Within Us Strongyloides stercoralis – Endemic to temperate southern United States – Causes gastrointestinal problems, Loeffler’s syndrome Taenia solium (pork tapeworm) – Mostly seen in southwestern United States – Transmitted by eating undercooked pork Giardia lamblia – Outbreaks of giardiasis in child care centers

Vaccinations Yet to Crunch Numbers….. (1 of 2) Polio is now endemic only to Afghanistan, India, Pakistan, and Nigeria. – Thanks to global eradication efforts A rabies virus vaccine was prepared in the 18 th century by Louis Pasteur. – Disease is still not contained because there is no specific treatment.

Vaccinations Yet to Crunch Numbers….. (2 of 2) Hepatitis B – Can cause fatal liver disease during acute stage. – Almost 2 billion people are infected worldwide. – Chemotherapeutic solutions for treatment are yet to be discovered. – Acute incidences are being tackled with measures like education, sterile needles for drug abusers, and blood products screening.

Use of Microbes in Biological Warfare Biological weapon use dates back to at least 600 B.C. Many countries have produced such weapons. – Including Germany, the United States, Russia, Japan, Iraq Weapons today include anthrax, smallpox, and Ebola virus.

Hepatitis C Virus Causes liver problems Contagious Transmitted through contact with blood, needle stick injuries, needle sharing by drug abusers, sexual contact Treated with preventive measures and drugs such as interferon and ribavarin

Outbreaks in the United States (1 of 2) H 1 N 1 influenza virus (swine flu) – Declared a pandemic in 2009 – Vaccine is available – Global Influenza Surveillance network monitors Salmonella outbreaks – Caused by contaminated peanut butter, tomatoes, jalapeno peppers, cilantro

Outbreaks in the United States (2 of 2) Measles outbreak in 2008 – United States declared measles absent from country in – Globalization led to transport of measles virus from another region. – Victims from the outbreak had not received measles, mumps, and rubella vaccination.